Event with no handler-method throws exception?

[TMattC]

Hi! I have defined an event in a certain class:

public class BrokenPackageReceivedEventArgs : EventArgs
{
private readonly byte[] package;
public byte[] Package { get { return package; } }
public BrokenPackageReceivedEventArgs(byte[] _package) { package = _package; }
}

public event EventHandler BrokenPackageReceived;

// Trigging the event:
BrokenPackageReceived(this, new BrokenPackageReceivedEventArgs(dataLst.ToArray()));

It seems that if no method is added to the event, it throws a NullReferenceException. I dont want that exception to occur, in fact I am baffled it actually does occur. Is this really the way events always do if no method is attached? Should I just use a try-catch with an empty catch to get rid of it, or am I missing something?

[TMattC]

I just realized I can do like this:

if(BrokenPackageReceived != null)
BrokenPackageReceived(this, new BrokenPackageReceivedEventArgs(dataLst.ToArray()));

Is this the common way to do it?

[Lost User]

Yes it is. And you could improve it a bit further by making a copy of it before you check it for null: var copy = BrokenPackageReceived; if(copy != null) copy(this, new .....); ..because theoretically some subscriber could unsubscribe during the execution of the null-check. edit: to clarify, not some subscriber but the last subscriber

[Pete OHanlon]

Rather than doing this, try this:

var handler = BrokenPackageReceived;
if (handler != null)
{
handler(this, new BrokenPackageReceivedEventArgs(dataLst.ToArray());
}

The reason you will want to do this is that there's a potential race condition because it's possible for BrokenPackageReceived to have a value when you check it, and then be null when you attempt to call it.